The research proposed will develop a new method to study short-lived complexes in solution. The study of nuclear relaxation times, arising from the coupling of solvent molecules with paramagnetic species (spin labels), will provide detailed information about the dynamics of intermolecular interations on the 10 to the minus 8th power to 10 to the minus 11th power second time scale. At present no method exists by which such short-lived interactions can be examined directly. The experimental program will 1) develop the instrumentation capable of measurement of fast nuclear relaxation times at multiple field strengths, 2) test the mathematical model used to describe the complexation, 3) examine the dynamics and mechanisms of simple nitroxide interactions with water and benzene, 4) apply the method to studies of hydrogen bonding in solution, and 5) investigate in detail the variables that determine the strength and lifetime of labile complexes such as those held by hydrogen bonds. The goal will be to determine the rates of forming and breaking these bonds between solute and solvent, and to isolate the parameters that effect changes in bonding strength and dynamics. Interactions such as hydrogen bonding are extremely significant in physical chemistry and health-related sciences because they determine the nature of liquids in general and specific properties of the systems under investigation.